From the Magic Kingdom to Epcot to Disney's Hollywood Studios, there are three little circles -- a head and the two mouse ears -- hidden in carpet patterns, tiles, wallpaper and even in the gift shops.

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Hunting for Mickey Mouse Hidden in Disney World

"Whenever you are on Disney property, anywhere in the world, always look around you in the details because Mickey will be hiding there," Barrett said.

There's a utility hole cover with mouse ears in Disney's Animal Kingdom. In the lobby of the Polynesian Resort a giant Mickey pattern is hidden in the stone floor slate. Walk a few more feet and the carpet has a Mickey here and there. Over in Epcot, a statue high up on a building in Germany has a Mickey on his crown.

Barrett, has mapped out nearly 1,000 of these hidden characters throughout the theme park and included them in a book: Hidden Mickeys, A Field Guide to Walt Disney World's Best Kept Secrets. The search for the Mickeys is so popular that the book is in its fourth edition with a fifth soon on the way. (It's available at Walt Disney World gift shops for $12.95.)

And just in case you were wondering, yes Barrett, 59, does have a day job as a physician. And no he wasn't always a theme park fan.

He first ended up at Disney World for a medical conference in January of 1989. He brought along his wife Vickie and their then five-year-old son Steven. On the plane, he started reading a guidebook that Vickie bought and was suddenly hooked, dragging the family around the parks.

"It was love at first sight," he said. "I was not theme park person but moved to Orlando in 1998 to be close to Disney World."

Searching for Mickey Mouse at Walt Disney World

Now, thanks to an annual pass, he visits the parks often.

"Since 1998, every other week," Barrett said. "That's a lot of times."

So why the obsession?

"It's just a fascinating game that Disney plays with the guests and I just happen to play the game well," he said laughing.

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Bob Sehlinger, co-author of The Unofficial Guide to Walt Disney World said that the Disney really encourages people who like to find different ways to explore the parks. Some folks like to collect autographs of characters, he said, others look for hidden Mickeys.

"These folks are really paying attention to the details. A lot of these are not easy to find," he said. "I don't think these people are crazy. The Disney faithful really love the detail that Disney builds into everything it does."

Sehlinger said the Mickeys are cleverly hidden or camouflaged but "very clear once you see it."

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"The way most people look for hidden Mickey's is during their downtime, walking the park from one attraction to another or while standing in queue," he said. "There's all sort of level of detail that escapes the average visitor at Walt Disney World."

Hidden Mickey Search

Barrett started collecting information about the hidden Mickeys in 1999 and wrote the first edition of his book in 2002. These days, most of the tips about Mickeys come in through his website and with discussions with park employees, known as cast members. (Disney is the parent company of ABC News.)

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"I get e-mails every day from hidden Mickey hunters," he said.

Barrett personally verifies every Mickey tip he receives. But not every hidden Mickey is legitimate. Some are just regular Mickeys that are clear to everybody -- there needs to be some creativity and work needed to find them. Others might be three circles nearby but not in the correct proportions.

"Sometimes it's wishful thinking; sometimes it's more of a decorate Mickey," he said.

Only about one in every four pans out. If one is questionable, Barrett asks his online followers to vote.

"The voters are usually as discriminating as I am," he said.

And not all hidden characters are Mickey. For instance, in the rocks on the left side of the Big Thunder Mountain exit a Tinkerbell silhouette can be found carved into the rocks.

"The story goes that hidden Mickeys started at Epcot," Barrett said. "When Epcot was being built, Walt Disney management did not want characters in Epcot. They wanted to keep them in the Magic Kingdom. So, the imaginers began hiding Mickeys in Epcot attractions."

From there, they have expanded to the other parks, restaurants and hotels in Florida, California and around the world.

Barrett said going to Disney World helps him deal with his workplace stress and makes him feel like a kid again. But don't assume that when he goes home, he stops thinking about Mickey.

"I dream about hidden Mickeys," he said. "I see them in clouds. I see them off Disney property. I'm looking for them everywhere."